In Voice over Internet Protocol (VoIP), packetized voice data flows over the Internet, a general-purpose packet-switched network, instead of traditional dedicated, circuit-switched voice transmission lines, such as the public switched telephone network (PSTN). VoIP over WLAN is where WLAN network architecture, such as IEEE 802.11x protocol, is utilized as the final segment of the packet switched portion of the transport sequence.
Referring to FIG. 1, an exemplary VoIP over WLAN communication system 100 is shown. A WLAN access point 100 provides wireless network capabilities to various wireless transmit/receive units (WTRUs) 110A, 110B. In this exemplary implementation, WTRU 110B is a VoIP handset. The WLAN portion of the system 100 is designated as 101. The WLAN access point 105 provides access to the Internet 120 by way of a modem 130. A gateway 140 connects the packet switched domain 102 to the circuit switched domain 103, and converts packet switched data to circuit switched data. A typical circuit switched network for handling voice telephone communications is the public switched telephone network (PSTN) 150. The gateway 140 connects the Internet 120 to the PSTN 150. A standard wired telephone 160 completes the system.
In typical data applications over Internet Protocol (IP) networks, data flows are generally asymmetric. That is, the quantity of data downloaded from the Internet is typically much greater than the quantity of data uploaded to the Internet. In contrast, in a typical VoIP implementation, such as the exemplary one shown in FIG. 1, data flows are generally symmetric. The nature of voice communications requires that the amount of data flowing to the VoIP handset 110B be roughly equivalent to the amount of data flowing away from the VoIP handset 110B, of course depending on the loquaciousness of the users. Data flow symmetry is a particular problem in the wireless WLAN portion of the VoIP system. Compounding this problem, IP does not provide any mechanism to ensure that data packets are delivered in sequential order. Time sensitive applications, such as VoIP, are faced with the task of restructuring streams of received packets which may be received out of order or missing packets altogether. Ensuring a consistent audio stream with minimal latency is required for packet based voice applications.
Quality of Service (QoS) refers to the capability of a network to provide priority to selected network traffic. QoS is typically implemented in various types of networks including Frame Relay, Asynchronous Transfer Mode (ATM), Ethernet and 802.x networks, SONET, and IP-routed networks that may use any or all of these underlying technologies. QoS methods provide varying levels of priority to individual data flows or packets including dedicated bandwidth, controlled jitter and latency, and improved loss characteristics. Real-time and interactive applications, such as VoIP, require a minimal QoS, or priority, in order to handle the symmetric nature of real-time voice communications, and to deal with inherent IP shortcomings such as disordered packets.
Therefore, an apparatus and a method for improving packet transmission generally and for reducing latency specifically in VoIP over WLAN is desired.